CVE-2026-49844 Apache Log4j API: Improper serialization of non-finite floating-point values in MapMessage.asJson()

What is CVE-2026-49844?

CVE-2026-49844 is a medium-severity vulnerability in Apache Log4j API, published on 10 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Improper encoding of non-finite floating-point values during MapMessage JSON serialization in Apache Log4j API produces output that is not valid JSON. This issue affects Apache Log4j API versions 2.13.1 through 2.25.4 and version 2.26.0.

The fix for CVE-2026-34481 did not cover all code paths: when a MapMessage contains a non-finite IEEE 754 value (NaN, Infinity, or -Infinity), MapMessage.asJson() emits the corresponding bare token. RFC 8259 does not permit these tokens, so a conformant parser rejects the resulting document.

The defect is reachable only when both of the following conditions hold:

* The application uses the message resolver https://logging.apache.org/log4j/2.x/manual/json-template-layout.html#event-template-resolver-message of JsonTemplateLayout or any other layout that relies on MapMessage.asJson() or MapMessage.getFormattedMessage(new String[]{"JSON"}). * The application logs a MapMessage that contains an attacker-controlled floating-point value.

An attacker who can supply a non-finite value can cause the affected layout to emit malformed JSON, which may corrupt the enclosing log record or disrupt downstream log ingestion and parsing.

Users are advised to upgrade to Apache Log4j API 2.25.5 or 2.26.1, both of which emit RFC 8259-compliant JSON for non-finite values.

Weakness: CWE-116

Which versions are affected by CVE-2026-49844?

4 open source packages ship an affected version, including org.apache.logging.log4j:log4j-api. It affects 1 product.

Products include Apache Log4j.

How do I fix CVE-2026-49844?

Upgrade org.apache.logging.log4j:log4j-api to a fixed version for your release line: 2.25.5 or 2.26.1.

Is CVE-2026-49844 being exploited?

There is no known exploitation of CVE-2026-49844 in the wild and no public exploit code.

Public exploit code: 1 proofs of concept on GitHub.

Other vulnerabilities in Apache Log4j API

• CVE-2021-44228 Apache Log4j2 Remote Code Execution Exploited Critical 10.0
• CVE-2021-45046 Apache Log4j2 Deserialization of Untrusted Data Exploited Critical 9.0
• CVE-2022-23305 SQL injection in JDBC Appender in Apache Log4j V1 Critical 9.8
• CVE-2017-5645 Deserialization of Untrusted Data in Log4j Critical 9.8
• CVE-2022-23302 Deserialization of untrusted data in JMSSink in Apache Log4j 1.x High 8.8

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as CLEANSTART-2026-AP60356, CLEANSTART-2026-HD36441, CLEANSTART-2026-KK56976, CLEANSTART-2026-OB90229, CLEANSTART-2026-ON00136, CLEANSTART-2026-PP78809 and 97 more.